Effects of Serial Dependence and Large-Scale Tropospheric Circulation on Midlatitude North American Terrestrial Carbon Dioxide Exchange

Abstract

Linear regression was used to relate modes of tropospheric circulation variability to estimates of gross ecosystem production (GEP) and ecosystem respiration (ER) measured at 14 midlatitude North American eddy covariance (EC) towers. The North Atlantic Oscillation (NAO) exhibited a north-south gradient in its effect on fluxes, with negative influence on fluxes at central and northeastern stations and positive influence on fluxes at southeastern stations. During spring, average values of GEP and ER within the northern "cold" sector decreased by 22 and 12 g C m Ϫ2 (18% and 11%), respectively, in response to a unit increase (ϩ1 standard deviation) in the expansion coefficient of the NAO mode. Despite a northward advancement of the "warm" sector during summer, GEP and ER remained negatively correlated with the NAO at northern stations, decreasing on average by 48 and 30 g C m Ϫ2 (8% and 6%), respectively. During spring, the North Pacific Oscillation (NPO) reduced GEP and ER at central and northeastern stations on average by 20 and 7 g C m Ϫ2 (16% and 6%) and increased GEP and ER at southern and west coast stations on average by 53 and 49 g C m Ϫ2 (12% and 17%) in response to a unit increase in the NPO. This pattern persisted into summer, only shifted northward, with flux decreases of 19 and 24 g C m Ϫ2 (3% and 5%) at northern stations and increases of 72 and 82 g C m Ϫ2 (9% and 16%) at central stations. The direction of the flux response in each case was supported by synoptic conditions inferred from composite maps of North American circulation and gridded surface air temperature anomalies. The magnitude and timing of the relationships differed between stations and was attributed to differences in geographic location and plant functional type. Difficulty in the interpretation of significant correlations was attributed to the short sample length of typical EC records and unmodeled variability, including, for example, modulation by the NAO during high NPO. Despite these limitations, long-term monitoring EC stations show promise in characterizing the regional and ecosystem-specific carbon cycle response to low-frequency modes of tropospheric circulation variability and may play a critical role in validating ecosystem model responses to such phenomena.

Influence of Low Frequency Variability on Climate and Carbon Fluxes in a Temperate Pine Forest in Eastern Canada

“…All other significant correlations were not found with the carbon fluxes from our site. Although these studies in the literature and our study identified a relationship between local climate oscillations and carbon exchanges, differences in our findings and that of Grant et al [67], Hember and Lafleur [68] and Zhang et al [16] could be attributed to differences in geographic locations, hydrological conditions and different forest species. Our study found a significant link between climate oscillations and carbon fluxes, where local climate conditions were modified by the regional circulation in the Great Lakes region in eastern North America.…”

“…Hember and Lafleur [68] investigated the connections between the NAO and the North Pacific Oscillation (NPO), another teleconnection pattern that is correlated with the ENSO, with surface air temperature, precipitation and carbon fluxes. Using eddy covariance flux data spanning 1994-2006 from mid-latitude North American ecosystems, they found that in the spring, correlation in the southeast stations was positive between NAO and surface air temperature, while the NPO was positively (negatively) correlated with temperature (precipitation) in the northeast.…”

Relationships between large-scale circulation patterns and carbon dioxide exchange by a deciduous forest

“…Several reasons may be responsible for the differences. The large-scale circulation patterns have different effects on climate at the three sites due to their different geographic location (Table 1), and CO 2 exchange responds differentially with respect to latitude and climatic variations [e.g., Nemani et al, 2003;Gong and Ho, 2003;Notaro et al, 2006a;Hember and Lafleur, 2008;Grant et al, 2009;Wharton et al, 2009]. Another possible reason is that the three AmeriFlux research sites have different forest composition species, which affects the response of CO 2 exchange to the climate [e.g., Hadley et al, 2009;Richardson et al, 2009].…”

“…In this study, the annual NEE of deciduousdominated Harvard Forest and Morgan Monroe State Forest exhibits significant correlations with climate indices in fall, while conifer-dominated Howland Forest NEE is closely linked to climate indices in winter and spring. Other characteristics of sites such as hydrological conditions, topography, disturbance, nutrient, and measurement errors may also introduce some differences [Hember and Lafleur, 2008;Grant et al, 2009;Hadley et al, 2009]. Moreover, the study periods for the three sites are different, but in all cases, the data length is short.…”

“…[4] Large-scale circulation patterns influence the location and intensity of synoptic atmospheric pressure systems, and thereby significantly modify northern midlatitude climate [e.g., Wallace and Gutzler, 1981;Barnston and Livezey, 1987;Hurrell, 1995Hurrell, , 1996 and ecosystems [e.g., Goldstein et al, 2000;Freedman et al, 2001;Morgenstern et al, 2004;Urbanski et al, 2007;Hember and Lafleur, 2008;Grant et al, 2009;Wharton et al, 2009]. Over the northeast United States, previous studies have demonstrated that the climate and circulation features are strongly influenced by large-scale circulation patterns in the Pacific, Atlantic and Arctic regions.…”